Logical node identification in an information transmission network

ABSTRACT

A system for generating and sending a Logical Node identification signal as part of a data stream is disclosed. The system also includes subscriber stations capable of receiving and extracting Logical Node identification information from a data stream. The subscriber stations create new messages including the Logical Node identification signal and send the message to the transmission network system control, such that switching of data streams to an appropriate channel over the information transmission network is done consistent with the network topology.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/663,256, filed on Sep. 16, 2003 now U.S. Pat. No. 7,203,201, which isa continuation of U.S. patent application Ser. No. 09/436,934, filed onNov. 8, 1999 (now U.S. Pat. No. 6,697,376), which claims the benefit ofU.S. Provisional Patent Application Ser. No. 60/109,341, filed Nov. 20,1998, which applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to the field of informationtransmission networks and more specifically to Logical Nodeidentification of such networks. More particularly, the presentinvention relates to Logical Node identification of such networkssupporting session based routing/switching of information flow inheterogeneous networks.

2. Description of the Background Art

In the field of information transmission, routing and switching ofinformation to the destination node is most commonly accomplished in oneof two approaches: (1) symmetric switched virtual paths/circuits (i.e.,ATM) or (2) packet-based routed networks (i.e. Internet). A third typeof information routing/switching network exists in many forms that canbe better supported through a variant of the two approaches withasymmetric switched virtual paths/circuits or asymmetric packet basedrouting.

This third area can be classified into two categories: first, the set ofinformation transmission networks that require a combination of thepacket routed networks tightly coupled with asymmetric switched networks(i.e. interactive multimedia content delivery such as in video-on-demandthat requires a streaming network flow for video and audio and usuallyan Out Of Band IP network to handle the interactivity between the sourceand destination); second, the set of information transmission networksthat can improve network latency by taking advantage of the knowledge ofthe point of access in packet based networks (i.e., dynamic routingchanges necessary to support unique roving lap top computers). Thepresent application will address this first case.

The former category of information transmission networks is what thepresent invention will address in detail. In particular, the interactivemultimedia service of video-on-demand over Hybrid Fiber Coax (HFC)networks is currently in existence for cable services. In this case,there exists unidirectional content streaming (QAM modulated video andaudio streaming of content to the digital set top box in the home) andIP based interactivity (via Out Of Band downstream to the home and avaried Return Path packet forwarding connectivity from the subscriber'sset top box to the cable headend equipment). This same solution can beused for satellite broadcast (content delivery) with wireless (cellphone) or telephone modem for interactivity; as well as for terrestrialbroadcast systems (e.g. MMDS, LMDS). It is also noted that the controlsession via the Out Of Band could also be multiplexed into the streaminglink in the In Band.

A technique to increase the number of video-on-demand programs that canbe concurrently transmitted is by channel reuse, where programs areassigned to channels at an intermediate node (typically referred to as a“remote headend” or “hub”) where lines from individual subscriberstations are coupled to the main CATV network. For the purposes of thepresent invention, the term “headend” is defined as any physical sitewhere modulation, demodulation, and processing (controlling, monitoring,etc.) equipment are kept and operated whether they be staffed with humanoperators or unstaffed sites that are remotely monitored whether theyrelate specifically to Cable or other transmission means such as MMDS.This technique allows the same channels to be assigned to differentprograms at different nodes (known as spectrum reuse through physicalmedia partitioning). Thus, dedicated video-on-demand channels cantransmit programs to one set of subscriber stations coupled to a firsthub, while the same channels can be used to transmit a different set ofprograms to another set of subscriber stations coupled to a second hub.

Typically, provision of video-on-demand services is implemented byassigning a session control manager (SCM) to one or more hubs. The SCMis responsible for receiving requests from set-top boxes at associatedhubs and providing the requested services. Each SCM must then beinformed of the subscriber stations corresponding to the assigned hub.Based on this topological information, the SCM provides the informationfor the creation of a virtual circuit from the video server to the QAMmodulator, and thus an access mechanism to the video and audio streamfrom the set top box. The SCM also tells the set top box which frequencyto tune the demodulator and which packet identification numbers (PIDs)to filter for the video and audio streams.

If subscriber stations are added or deleted, such as by new or canceledsubscriptions, then the mapping between SCMs, hubs, and set top boxesmay need to change. For example, a set of QAM channels can onlyaccommodate a certain number of subscriber stations. If the number ofsubscriber stations on a hub exceeds the capacity of the allocatedstream, then further Logical Node partitioning may occur on the hub.While such changes can be made to the mapping information in the headendmanually, it is desirable to have a more efficient and automated methodfor re-assigning channels for node usage.

SUMMARY OF THE INVENTION

In a principal aspect, the present invention provides automatictransmission to subscriber stations of information about correspondingsession control managers and coupling of channel groups defined asnodes.

In accordance with the principles of the present invention, avideo-on-demand (VOD) system includes a plurality of session controlmanagers to cause transmission of a requested program to a requestingsubscriber station. The video-on-demand system is coupled to a pluralityof subscriber stations by a network capable of spectrum reuse betweenthe subscriber station and a corresponding one of a plurality of nodesdisposed between the video-on-demand system and the subscriber station.The video-on-demand system comprises a Logical Node assignor whichassigns a logical identification to each of the nodes to identify acorrespondence between each of the nodes and a corresponding one of thesession control managers. For example, a Logical Node for HFC is definedas the group of Fiber Nodes that share the same QAM modulation spectrum.I.e. same streams in VOD channels.

In accordance with further aspects of the invention, the Logical Nodeassignor periodically transmits node assignment information to each ofthe nodes in the network to uniquely identify the Logical Node and alsoidentify a corresponding session control manager for each of the nodes.This allows the subscriber stations to tune to this digital channel atany time and get this information on a timely basis. Advantageously,such techniques allow automatic dissemination of information regardingmapping between session control managers, Logical Nodes, and subscriberstations. The result is reduced complexity and overhead in managing avideo-on-demand system, thereby reducing overall costs.

The principles of the present invention are particularly advantageous inHybrid Fiber Coaxial (HFC) systems used for transmission of videoprogramming. However, the principles described herein may also be usedin direct broadcast satellite (DBS) systems, Local Multi-PointDistribution Services (LMDS), and Multi-channel Multiunit DistributionSystems (MMDS).

One particular advantage of the present invention, is that because ofthe automatic identification of the Logical Node to which eachsubscriber station is associated, the present invention allows forswitching the unicast VOD stream to the correct QAM modulator thatmodulates to the Logical Node for receipt by the subscriber station.This is particularly advantageous as new Logical Nodes can be created orexisting nodes are divided because of increasing demand for subscriptionand service.

These and other features and advantages of the present invention may bebetter understood by considering the following detailed description of apreferred embodiment of the invention. In the course of thisdescription, reference will frequently be made to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a general embodiment of a system employingthe principles of the present invention.

FIG. 2A is a block diagram of a first embodiment of the system employingthe principles of the present invention where a broadcast satellite isused as a portion of the transmission network.

FIG. 2B is a block diagram of a second and preferred embodiment of thesystem employing the principles of the present invention where anvideo-on-demand network is used as the transmission network.

FIG. 3 is a high-level block diagram showing a headend including sessioncontrol mangers, the hubs and the subscriber stations of the secondembodiment in more detail.

FIG. 4 is a high-level block diagram showing the session controlmangers, the hubs and the subscriber stations of FIG. 3 and the LogicalNodes into which they are divided in more detail.

FIG. 5 is a flowchart of a general method for transmitting Logical Nodeidentification signals and using them to configure the system andtransmit data signals.

FIGS. 6 and 7 are flowcharts showing operation of the system inaccordance with the principles of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, a preferred embodiment of a system 100 aconstructed in accordance with the present invention is shown. Thesystem 100 a preferably comprises: a Logical Node Identification (ID)generator 102, a signal source 104, a combiner 106, an informationtransmission network 108, and an information distributor 110. Thepresent invention is particularly advantageous because it inserts aLogical Node identification signal into the data stream. This LogicalNode identification signal is transmitted through the network 108, andthen retransmitted back to the SCM 224 (See FIG. 2B) for determining theprecise configuration of the system 100 a.

This first embodiment illustrates the most general implementation of thepresent invention, and therefore, will be described here in only generalterms. FIGS. 2A and 2B illustrate more particular embodiments of thepresent invention for specific transmission networks and will bedescribed with more particularity.

The Logical Node ID generator 102 produces at least one unique LogicalNode identification number and transmits the unique identificationnumber as a signal at the output of the Logical Node ID generator 102.Preferably, the Logical Node ID generator 102 produces a plurality ofunique identifiers which are sent to the combiner 106 and combined withother information according to which node or location to which theinformation is being transmitted. The output of the Logical Nodegenerator 102 is coupled to an input of the combiner 106. A signalsource 104 providing video, sound or data signals such as in a digitalvideo signal is provided as the output of the signal source 104, andalso provided to the combiner 106. The output of the signal source 104is coupled to the second input of the combiner 106.

The combiner 106 has one more outputs coupled to an informationtransmission network 108 for transmitting a combined signal thatincludes an address for the information, content from the signal source104, and the Logical Node ID signal from the Logical Node ID generator102 to the information distributor 110 coupled at the remote end of thetransmission network 108. In the preferred embodiment, the transmissionnetwork 108 includes one or more stream channels 202 for transmittinginformation from the combiner 106 to the devices downstream on theremote end of the information transmission network 108. The informationtransmission network 108 also includes configuration control channels204 for sending signals along a reverse path between the informationdistributor 110 and combiner 106.

The information distributor 110 is coupled to send and receive signalsover the information transmission network 108. The informationdistributor 110 is also coupled to a plurality of devices (not shown)such as set top boxes by a plurality of signal lines 120-132. Theinformation distributor 110 receives the streaming channels and sendsthe source signal and the Logical Node ID down a corresponding one ormore signal lines 120-132 according to the node ID number. For example,a group of signals sent over the information transmission network 108and received by the information distributor 110 having video content anda Logical Node ID number of 1 would be transmitted only over signal line120. Such video content and a Logical Node ID are not transmitted overother signal lines 122-132 for nodes 2-n. Other combined signals wouldbe similarly sent over the respective signal lines 122-132 correspondingto their Logical Node identification number. As shown, an individualLogical Node identification number such as Logical Node 4, maycorrespond to a plurality of signal lines such as signal lines 126, 128,130. In one embodiment, the signal lines 120-132 may be constructed ofhybrid/fiber coax. Thus, the information distributor 110 effectivelyseparates the data streamed over the streaming channels 202 fordistribution over individual signal lines or groups of signal linesconsistent with channel reuse.

The information distributor 110 also receives a plurality of signalssent upstream by devices (not shown) to the information distributor 110.The information distributor 110 in turn sends the signals over theconfiguration and control channels 204 to the combiner 106. In thismanner, a particular set top box (STB 220 see FIG. 2B) or subscriberstation can receive a signal including the Logical Node ID, incorporatethe Logical Node ID along with a signal identifying the subscriberstation, and send the incorporated signal upstream through theinformation distributor 110 and configuration and control channels 204to the combiner 106. Using this information, the SCM 224 determine theexact configuration of the network and nodes, make necessary changes(e.g. create new nodes, eliminate node or combine nodes) to maximize theusage of the network bandwidth.

Referring now to FIG. 2A, a second embodiment 100 b of the systemconstructed in accordance with the present invention is shown. In thesecond embodiment 100 b, like components having the same functionalityhave been labeled with like reference numeral for ease of understandingand convenience. The second embodiment 100 b includes the Logical NodeIdentification (ID) generator 102, the signal source 104, the combiner106, and a transmission network in the form of a streaming channel 202 aand a return channel 204 a. The information distributor takes the formof a receiver and descrambler 210 a, and a telephone 214 a.

The Logical Node Identification (ID) generator 102, the signal source104, the combiner 106 are the same as has been described above withreference to FIG. 1. However, in this embodiment, the combiner 106transmits the combined signal to a one or more base satellite stationsfor uploading to a satellite. The satellite in turn receives andtransmits the combined signal including the Logical Node ID to thereceiver and descrambler 210 a. While only one receiver and descrambler210 a is shown per satellite, those skilled in the area will realizethat there are preferably many receivers and descramblers 210 a for eachsatellite.

The receiver and descrambler 210 a receives the combined signal from thesatellite, descrambles the signal and sends the combined signal to oneor more devices 212 a coupled to the receiver and descrambler 210 a. Thereceiver and descrambler 210 a is also coupled by a telephone 214 a-214n and a phone line 204 a-204 n to the combiner 106. The path through thetelephone and a public switched network provides the return path. Thosefamiliar in the art will recognize that the telephone 214 a-214 n andphone line 204 a-204 n could be a cell or wireless telephone. Thus, thereceiver and descrambler 210 a is able to communicate with the devices212 a to determine channel selection and node ID and send thatinformation back to the combiner 106 via the telephone line 204 a-204 n.In this manner, the system 100 b may define a plurality of LogicalNodes, change or modify the nodes as desired and confirm the networkconfiguration through use of the Logical Node ID signal inserted by thecombiner 106 and returned by the device 212 a-212 n and the receiver anddescrambler 210 a-210n.

Referring now to FIG. 2B, a third and preferred embodiment of a system100 c constructed in accordance with the present invention is shown. Thethird embodiment 100 c uses the capabilities of a traditional cablesystem to provide the streaming channel 202 b and the return channelprovided with video-on-demand systems as the return path. The thirdembodiment 100 c preferably comprises a Logical Node Identification (ID)generator 102 b, a video server 104 b as the signal source, a combinerin the form of a digital video modulator (DVM) module 106 b, the opticalfiber 202 b as the transmission network, a control channel modem (CCM)222 and a session control manager (SCM) 224 providing the return path204 b, and an information distributor 110 b. The system 100 cadvantageously uses a plurality of DVMs 106 b and each has a pluralityof channels. Each DVM 106 b preferably provides the video streams todifferent Logical Nodes. Thus, the automatic identification of theLogical Node in the return channel, allows the SCM 224 to determinewhich video stream and channel provided by which DVM corresponds to aparticular set top box 220. This is particularly advantageous becausethere is routinely a need to re allocated the set top box 220 amongLogical Nodes and DVM channels.

The DVM module 106 b receives video signal from the video server 104 band node ID signals from the Logical Node Identification (ID) generator102 b. The DVM module 106 b combines these signals and transmits themover the transmission channel 202 b to the information distributor 110b. The SCM 224 controls the mixing of content provided by the videoserver 104 b and receives communication over the back or return path 204b via CCM 222. For example, some of these components may be found at aheadend in a typical on-demand cable system. The information distributor110 b divides the signals received from the DVM module 106 b and outputsthem over respective signal lines 120-132 according to the Logical NodeID assigned to each signal. For example, a plurality of set top boxes220 a-220 n are coupled to line 120 and form Logical Node 1. Each of theother signal lines 122-132 or groups of the signal lines are coupled insimilar fashion to form Logical Nodes of the network. Such any exemplarysystem is described in more detail in U.S. Pat. No. 6,253,375, issuedJun. 26, 2001, entitled “System For Interactively DistributingInformation Services,” filed Dec. 4, 1997, which is incorporated hereinby reference.

In this third embodiment 100 c, the Logical Node generator is preferablypart of a transport processing module 102 b. The transport processingmodule (TPM) 102 b adds control signals and data to the streamsgenerated by the DVMs 106 b. The TPM 102 b is preferably coupled to thesession control manager 224 and to the CCMs 222 through the VME busarchitecture. The TPM 102 b is also coupled to the DVM module 106 b toprovide for in-band communication. More specifically, the TPM 102 b alsoadds identification information to the video and audio content providedby the server 104 b such as program specific information (PSI) andpacket identification numbers (PIDs).

In FIG. 3, a plurality of subscriber stations 305-308 are coupled by aninformation transmission network 302 to a cable headend 304 forreceiving video programming services. The subscriber stations 305-308preferably take the form of a digital set-top box capable of requestingvideo programming from the headend 304. However, the subscriber stations305-308 can take other forms to provide information from network 302 todifferent types of output devices, e.g. cable modems with personalcomputers and ADSL modems with set top boxes. The subscriber stations305-308 are shown generally and each shown subscriber station 305-308represents a plurality of subscriber stations.

The headend 304, which is shown only in very general form, includes thenecessary equipment and capability to provide subscriber stations305-308 with on demand services such as, for example, video-on-demandservices where a user requests a particular movie through a subscriberstation and the headend 304 responds by transmitting data representingthe movie to the requesting subscriber station for viewing by the user.Included within the headend 304 are a plurality of session controlmanagers (SCMs) 314, 315, 316 and 317. The SCMs perform various systemcommand and control functions as well as communicating the requestedprogramming in the form of a data stream to the transmission network302. The SCMs 314, 315, 316 and 317 have capability to address thestreams to be propagated to the subscribers in broadcast, multicast orunicast modes. As used herein, the term “broadcast” means transmissionof data for receipt by all subscriber stations on the network. “Unicast”means transmission of data for receipt by only a single subscriberstation on the network, and “multicast” means transmission ofinformation for receipt by more than one but less than all subscriberstations on the network.

Specifically, each SCM 314-317 transmits video signals to the subscriberstations over an information channel in network 302 by modulating a baseband data stream onto a carrier signal and up converting the signal to atransmission frequency that complies with a conventional CATV frequencyspectrum. By way of example, a downstream data modulation performed by aSCM can be a 64-ary Quadrature Amplitude Modulation (QAM) and thetransmission frequency can be in the range of 54-860 MHz. Thesetechniques are merely exemplary of a typical transmission mechanism andother modulation types and frequency bands may be used.

The SCMs 314-317 transmit control information to the subscriber stations305-308 via a downstream command channel in transmission network 302. Byway of example, such control information can be frequency multiplexedwith the information channel to effect transmission on a carrier in therange of 54-860 MHz using a 1 MHz bandwidth. The subscriber stations305-308 communicate with a corresponding SCM 314-317 via a reverse (backor upstream) channel. In an exemplary embodiment, each SCM 314-317supports 16 such reverse channels. Each reverse channel carries, forexample, a BPSK modulated signal on a carrier in the range of 5-42 MHz,where the channel capacity is approximately 64 Kbps. The exact frequencyranges, modulation types or channel capacities are not critical and canbe varied. Further details of the operation of the SCMs 314-317 andother components of the headend 304 to provide VOD services aredescribed in U.S. Pat. No. 6,253,375, issued Jun. 26, 2001, and entitled“System for Interactively Distributing Information Services”, andassigned to the assignee of the present application, which is herebyincorporated by reference in its entirety.

The transmission network 302 preferably takes the form of a Hybrid FiberCoaxial (HFC) network in which the headend 304 is coupled to the hubs309-312 by fiber optic cabling. The hubs 309-312 are coupled tocorresponding subscriber stations by coaxial cabling. Each hub 309-312typically has capability to support hundreds to thousands of subscriberstations. The hubs 309-312 are preferably of conventional type.

The VOD service employs a number of predetermined channels in theinformation channel to transmit the requested video programs. By way ofexample, the number of channels available for use by the VOD service canbe 2, 4, or 8 analog channels. The network 302 and headend 304 implementspectrum reuse at the hubs 309-312 to increase the number of channelsavailable for the VOD service.

Each of the Logical Nodes (VOD channels per hubs 309-312) has acapability to service a limited number of subscriber stations. Thenumber of Logical Nodes required is therefore roughly proportional tothe number of subscribers being serviced by the system 100 c. By way ofexample, each 64-QAM channel typically can service up to 80 subscribers.Depending upon the number of subscriber stations coupled to a particularhub 309-312, a particular Logical Node may service only a portion of thesubscriber stations on a hub, may service all of the subscriber stationson a hub but no more, or may service subscriber stations on more thanone hub. Each of these scenarios is shown in FIG. 3. For example, SCM314 services subscriber stations on hubs 309 and 310. This wouldtypically occur in a situation where the hubs 309 and 310 are not fullypopulated with subscriber stations 305, 306 or where initial servicepenetration is low. SCM 315 services only subscriber stations 308 on hub312. Hub 311 has associated therewith SCMs 316 and 317 for servicingsubscriber stations 307. This situation arises where a hub has coupledthereto, a number of subscriber stations that exceed the capacity of aparticular SCM and requires many Logical Nodes. As the number ofsubscriber stations increases or decreases for a particular hub, themapping between SCMs Logical Nodes, and subscriber stations may need tochange. For example, this may happen if new homes are built or ifexisting subscribers cancel subscriptions to services offered by headend304 or if new subscribers are added.

In accordance with the principles of the present invention, SCMs 314-317can be automatically allocated to subscriber stations 305-308 based onthe changing topology of the network 302 and its associated subscriberstations. Advantageously, this is performed by determining the number ofsubscriber stations coupled to each hub, and transmitting a Logical Nodeidentifier (ID) to each subscriber station. The Logical Node ID providesa correspondence between an SCM and corresponding subscriber stations.For example, in FIG. 4, subscriber stations 305 and 306 correspond to afirst Logical Node from nodes 1-4, subscriber stations 307 correspond toat least two (third and fourth) Logical Nodes one from nodes 11-20 andthe other from nodes 21-n, and subscriber stations 308 correspond to asecond Logical Node from nodes 5-10. 1-4, subscriber stations 307correspond at least two (third and fourth) Logical Nodes and from nodes11 -20 and the other from nodes 21-n, and subscriber stations 312correspond to a second Logical Node from nodes 5-10.

The Logical Node IDs for the subscriber stations on the network 302 arepreferably determined periodically and periodically transmitted to thesubscriber stations. Preferably the Logical Node ID is transmitted as aMPEG-II (Motion Pictures Expert Group, Type II) packet which containsappropriate header information together with the Logical Node ID. MPEGtype encoding is a common protocol for encoding video data and istherefore a convenient protocol for encoding of the Logical Node ID.However, the exact manner in which the Logical Node ID is encoded fortransmission is not critical and other encoding techniques can be usedwithin the principles of the present invention.

FIG. 4 of the drawings illustrates, by way of the example shown in FIG.3, the manner in which the Logical Node IDs are transmitted. In FIG. 4,subscriber stations 305 and 306 are part of a first Logical Node. Thisinformation is provided to subscriber stations 305-306 by transmittingLogical Node ID 1 from headend 304 to subscriber stations 305-306.Subscriber stations 308 are part of second Logical Node. Thisinformation is provided to subscriber stations 308 by transmittingLogical Node ID for this second Logical Node from headend 304 tosubscriber stations 308. Subscriber stations 307 are either part of athird Logical Node or fourth Logical Node. The corresponding nodeinformation (third Logical Node ID or fourth Logical Node ID) istransmitted to the appropriate subscriber stations 307.

The introduction of the Logical Node ID into the video stream and itsuse to identify the channels servicing a particular subscriber stationare particularly advantageous. The provision of Logical Node ID signalsin the video stream allow the subscriber stations to be moved anywherein the network and get the video streams switched to the subscriberstation based on a new Logical Node ID. For example, a particularsubscriber station may be initially connected to the network andassigned to Logical Node ID 1. All the information for the subscriberincluding information particular to the subscriber station is provided.However, the user may move geographically, take the subscriber stationand attempt to gain access from a new location being service by adifferent Logical Node. Since the ID of the different Logical Node ispart of the stream, once it is provided to the relocated subscriberstation, the headend 304 will know which channels to provide signalsintended for the user. This eliminates any manual reconfiguration of thenetwork that is required in the prior art. Rather with the presentinvention, the service can be updated by simply updating channel and DVMinformation in the SCM. Other examples where the provision of theLogical Node ID is particularly advantageous is where new nodes arecreated or eliminated by changes in the number of subscribers usingparticular channels. The use of Logical Node ID eliminates the need forany changes in manual configurations.

Referring now to FIGS. 5-7, the methods of the present invention forsending and using a Logical Node ID signal as part of streaming datawill be described in more detail. The general method will first bediscussed with reference to FIG. 5. Then a method for using the LogicalNode ID to determine the appropriate channel on which to transmit arequested program is described in two embodiment with reference to FIGS.6 and 7.

As shown in FIG. 5, the method for inserting, transmitting and using theLogical Node ID in accordance with the present invention is shown. Theprocess begins in step 502 by generating a unique Logical Node ID foreach node and inserting such Logical Node ID into the data stream. Thenin step 504, the Logical Node ID signal is transmitted as part of thedata stream over the information network 108. Next, in step 506, thedata stream including the Logical Node ID is received at a subscriberstation. Then in step 508, the subscriber station uses the Logical NodeID received to create a new message which includes the Logical Node ID.The message created in step 508 is then sent in step 510 to the headend.The combiner or headend sets the Logical Node membership using thismessage in step 512, and thus, the topology of the network is known bythe system 100 c. The system 100 c can then use the information storedat the headend to switch data streams using the TPM 102 b and DVM module106 b such that programs will be correctly routed even though changesmay have been made to the network manually or automatically. In otherwords, using the Logical Node ID the TPM 102 b and DVM module 106 b canbe assured to send data to the appropriate subscriber stations.

FIG. 6 is a flowchart showing an embodiment where the role of the masterSCM in identifying the corresponding SCM and the role of the hub inproviding the channel allocation information to the subscriber stationare eliminated. Advantageously, elimination of such actions reduces theamount of time (and accompanying bandwidth) required to initiate VODservice. These steps are eliminated by storing the address of thecorresponding SCM together with the channel allocation information inthe subscriber station. This information can be stored in the subscriberstation in a nonvolatile memory such as a flash memory as typicallyfound on subscriber stations such as digital set-top boxes.

Turning to FIG. 6, at step 602, the user requests VOD by way of thecorresponding subscriber station. At step 604, the subscriber stationreads the Program Map Table (PMT) and at step 606 receives the periodictransmission of the Logical Node ID. At step 608, the IP address of theSCM, which is stored in the subscriber station and its listener portnumber are used to make a User Datagram Protocol (UDP orTCP—Transmission Control Protocol) connection between the SCM and thesubscriber station. At step 610, the program transmission occurs untiltermination at step 612.

FIG. 7 is a flowchart showing communication between a set-top box(portion of a subscriber station) and the headend 304 to request and toreceive video-on-demand (VOD) services, such as transmission of moviesor other video programs. At step 702, the user requests VOD services, byentering appropriate inputs into the set-top box. At step 704, thecorresponding hub responds to the request for VOD service byidentifying, from information stored in the hub, an SCM that isfunctioning as a master SCM. At step 708, the subscriber stationinitiates communication with the master SCM to establish a connectionbetween the master SCM and the subscriber station. This connection ispreferably established in accordance with the User Datagram Protocol(UDP) of the TCP/IP suite of protocols. At step 710, the hub allocates achannel for transmission of the requested video program from thecorresponding hub to the subscriber station. Also at step 710, themaster SCM allocates a program identifier (PID) to uniquely identify therequested program. Transmission of the Logical Node ID at step 712 isperformed periodically, such as for example, every one-tenth of asecond, and the Logical Node ID can therefore be expected to be receivedby the subscriber station. In an alternate embodiment shown in FIG. 7 bydashed lines, the channel for transmission of the requested videoprogram from the corresponding hub to the subscriber station, and theprogram identifier (PID) may be predefined (step 730). For example, acopy of a distributed packet having the predefined channel and PID maybe stored at the subscriber station using local storage to reduce thelatency in starting interactive sessions where the contents providetemporary copies of the information contained in the distributed packet.In such a case, steps 700-710 may be replaced with the single step 730of identifying the predefined channel and PID after which the methodcontinues with that information in step 714.

Once the subscriber station receives the Logical Node ID, it has thenecessary information to communicate with the corresponding SCM, and atstep 714 the UDP connection between the master SCM and the subscriberstation is terminated. At step 716, a UDP connection is establishedbetween the identified SCM and the subscriber station. Once establishedat 716, transmission of the requested program by the SCM to therequesting subscriber station occurs 718 until the transmission isterminated at step 720.

It is to be understood that the specific mechanisms and techniques whichhave been described are merely illustrative of one application of theprinciples of the invention. Numerous additional modifications may bemade to the methods and apparatus described without departing from thetrue spirit of the invention.

1. An apparatus for responding to a program request, the apparatuscomprising: a modulator; a session control manager; a processor; andmemory storing computer-readable instructions that, when executed by theprocessor, cause the apparatus to: periodically provide a logical nodeidentifier to a plurality of remote stations including a requestingremote station, wherein the logical node identifier identifies acorrespondence between a hub having the plurality of remote stations andthe session control manager, and wherein the session control manager,responsive to the program request from the requesting remote station, isconfigured to provide frequency and packet identification numbers(PIDs), indicative of a requested program, to the modulator, and whereinthe modulator is configured to transmit the requested program forreceipt by the requesting remote station, and wherein the sessioncontrol manager is configured to receive the logical node identifierfrom the requesting remote station.
 2. The apparatus of claim 1, whereinthe session control manager is configured to select a channel on whichthe requested program is transmitted using the logical node identifierreceived from the requesting remote station.
 3. The apparatus of claim2, further comprising: memory storing a mapping between the requestingremote station and the selected channel on which the transmission of therequested program occurs.
 4. The apparatus of claim 1, furthercomprising: a combiner configured to determine the correspondencebetween the hub corresponding to the requesting remote station and thesession control manager using the logical node identifier received fromthe remote station.
 5. The apparatus of claim 4, wherein the sessioncontrol manager, responsive to another program request from therequesting remote station, is configured to provide frequency and PIDsindicative of the another requested program to the requesting remotestation using the correspondence between the hub corresponding to therequesting remote station and the session control manager.
 6. Theapparatus of claim 5, wherein the modulator is configured to transmitthe another requested program for receipt by the requesting remotestation using the correspondence between the hub corresponding to therequesting remote station and the session control manager.
 7. Anapparatus comprising: a processor; and memory storing computer-readableinstructions that, when executed by the processor, cause the apparatusto: receive, from a remote station coupled to the apparatus by anetwork, a request for a program; assign a channel for transmission ofthe requested program to the requesting remote station; transmit, to therequesting remote station, a unique identifier for the requestedprogram; transmit, to the requesting remote station and a networkcontroller, a logical identifier that uniquely identifies the networkcontroller as the network controller corresponding to the requestingremote station; and transmit, to the requesting remote station, therequested program in response to receiving, from the requesting remotestation, a message indicating the logical identifier, wherein, theapparatus is configured to connect to the network controller via atleast one channel having a first bandwidth and a second bandwidth, thesecond bandwidth being lower than the first bandwidth.
 8. The apparatusof claim 7, further comprising: a master session control managerconfigured to receive the message indicating the logical identifier andassociate the requesting remote station with a logical node, wherein thelogical node is identified by the logical identifier.
 9. The apparatusof claim 7, further comprising: a master session control managerconfigured to assign one of a plurality of other session controlmanagers to cause transmission of the program identifier, the logicalidentifier and the requested program in response to receiving therequest for the program.
 10. The apparatus of claim 9, wherein themaster session control manager is configured to cause a correspondingone of the other session control managers to transmit requested programsto the requesting remote station using the logical identifier indicatedin the message received from the remote station.
 11. The apparatus ofclaim 9, wherein the master session control manager is configured toselect a modulator and a channel for transmitting requested programs tothe remote station using the logical identifier indicated in the messagereceived from the remote station.
 12. The apparatus of claim 9, whereinthe master session control manager is configured to switch, using thelogical identifier indicated in the message received from the remotestation, from a first modulator and a first channel for transmittingrequested programs to the remote station to a second modulator and asecond channel for transmitting requested programs to the remotestation.
 13. The apparatus of claim 7, wherein the memory storingcomputer-readable instructions that, when executed by the processor,cause the apparatus to: provide the unique identifier for the requestedprogram; and generate the logical identifier transmitted to the remotestation, wherein the apparatus further comprises a combiner configuredto combine the unique identifier and the logical identifier fortransmission to the remote station.
 14. A method comprising: providing alogical node identifier to a plurality of remote stations including arequesting remote station, wherein the logical node identifieridentifies a correspondence between a hub having the plurality of remotestations and a session control manager; responsive to a program requestfrom the requesting remote station, transmitting, by a computing devicehaving at least one processor, frequency and packet identificationnumbers (PIDs) to the requesting remote station, wherein the frequencyand PIDs are indicative of the requested program; receiving the logicalnode identifier from the requesting remote station; and transmitting therequested program for receipt by the requesting remote station.
 15. Themethod of claim 14, further comprising: selecting a channel fortransmitting the requested program using the logical node identifierreceived from the remote station.
 16. The method of claim 15, furthercomprising: storing a mapping between the requesting remote station andthe selected channel.
 17. The method of claim 14, further comprising:determining the correspondence between the hub corresponding to therequesting remote station and the session control manager using thelogical node identifier received from the remote station.
 18. The methodof claim 17, further comprising: responsive to another program requestfrom the requesting remote station, transmitting frequency and PIDsindicative of the another requested program to the requesting remotestation using the correspondence between the hub corresponding to therequesting remote station and the session control manager.
 19. Themethod of claim 18, further comprising: transmitting the anotherrequested program to the requesting remote station using thecorrespondence between the hub corresponding to the requesting remotestation and the session control manager.